1. Field of the Invention
The present invention relates to semiconducting yttrium-barium-copper-oxygen (YBCO) device in which semiconducting YBCO film is locally converted to a nonconducting YBCO film using a conductive atomic force microscope (AFM) and superconducting YBCO device in which superconducting YBCO film is locally converted to a nonsuperconducting YBCO film by an AFM, and manufacturing methods therefor.
2. Description of the Related Art
FIG. 1 is a graph showing the electrical characteristic of a typical semiconducting YBCO film, and FIG. 2 is a graph showing the electrical characteristic of a typical superconducting YBCO film. It can be seen that as the temperature falls, a semiconducting YBCO film shows a high resistivity, while a superconducting YBCO film shows superconducting properties, i.e., the resistivity drops to zero below a specific critical temperature. There are various factors that determine the semiconducting properties or superconductivity of YBCO films. As one of these factors, FIG. 3 shows experimental results, which indicate that the semiconducting and superconducting properties are dependent on oxygen content. More specifically, FIG. 3 shows the electrical properties with respect to changes in the value of parameter y where y=7xe2x88x92x in YBa2Cu3O7xe2x88x92x film. According to the experimental results shown in FIG. 3, a YBCO film shows semiconducting properties if yxe2x89xa66.3 while it shows superconducting properties if yxe2x89xa76.5. The YBCO material has difficulty in manufacturing tunnel junctions through dry or chemical etching due to its chemical sensitivity. Furthermore, it is well known that the material has a problem in high volume production since the characteristics between thus manufactured tunnel junctions are irregular. Accordingly, adoption of a planar patterning method which locally converts YBCO film through electrical or physical change is required.
To solve the above problem, it is a first objective of the present invention to provide a semiconducting yttrium-barium-copper-oxygen (YBCO) device which is locally converted by an atomic force microscope (AFM) in such a way as to electrically convert a portion of YBCO film, and a manufacturing method thereof.
It is a second objective to provide a superconducting YBCO device which is locally converted by an AFM in such a way as to electrically convert a portion of YBCO film, and a manufacturing method thereof.
Accordingly, to achieve the first objective, the present invention provides a semiconducting YBCO device locally converted by AFM which includes a MgO substrate, a semiconducting YBCO film stacked on the MgO substrate, a nonconducting YBCO region locally converted so as to form a tunnel junction in the semiconducting YBCO film, and electrodes which are formed at the ends of the semiconducting YBCO film.
The present invention also provides a method of manufacturing a semiconducting YBCO device locally converted by an AFM including the steps of: depositing a semiconducting YBCO film over a MgO substrate; forming electrodes at the ends of the semiconducting YBCO film, and placing an AFM tip on the semiconducting YBCO film between the electrodes and applying a predetermined voltage between the AFM tip and the electrodes to convert a local region of the semiconducting YBCO film contacted by the AFM tip to a nonconducting YBCO so that a tunnel junction may be formed in the local region of the semiconducting YBCO film.
To achieve the second objective, the present invention provides a superconducting YBCO device locally converted by an AFM including a MgO substrate, a superconducting YBCO film stacked on the MgO substrate, a nonsuperconducting YBCO region locally converted so as to form a tunnel junction in the superconducting YBCO film, and electrodes which are formed at the ends of the superconducting YBCO film.
The present invention provides a method of manufacturing a superconducting YBCO device locally converted by an AFM including the steps of: depositing a superconducting YBCO film over a MgO substrate; forming electrodes at the ends of the superconducting YBCO film; and placing an AFM tip on the superconducting YBCO film between the electrodes and applying a predetermined voltage between the AFM tip and the electrodes to convert a local region of the superconducting YBCO film contacted by the AFM tip to a nonsuperconducting YBCO so that a tunnel junction may be formed in the local region of the superconducting YBCO film.